Index: trunk/doc/developer/symbol_as_sheet.txt
===================================================================
--- trunk/doc/developer/symbol_as_sheet.txt	(nonexistent)
+++ trunk/doc/developer/symbol_as_sheet.txt	(revision 9000)
@@ -0,0 +1,18 @@
+Symbol loaded as a sheet
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Also known as: symbol edit mode or symedit.
+
+When this happens, sheet->is_symbol is set to 1 which triggers a bunch of
+special cases here and there. The general structure is this:
+
+- a symbol file is a single group (stored under a csch group in lihata)
+- when the loader detects this root, this group is loaded as sheet->direct
+- in sch-rnd sheet postproc some extra steps are done to load pens from the
+  default sheet, else all pens would be invalid; these pens are marked
+  ->copied_from_default=1
+- on save sheet->is_symbol decides only the direct group needs to be saved,
+  using the csch group root node instead of a sheet root
+- on save pens that are marked ->copied_from_default==1 are not saved
+  (undoable pen modify always resets this bit so any pen modification forces
+  saving the pen)